There is a constantly growing need for more effective insulating materials capable of withstanding the high temperatures encountered in modern day technology and which can be readily formed into a variety of shapes. A particular need exists in the area of melting, transporting and casting of non-ferrous metals where insulating materials must possess high strength, high resistance to erosion and wetting by the metal, good thermal shock resistance, and have good thermal insulating properties at the high temperatures encountered during use. In addition, the materials should be easy to use and relatively inexpensive.
Various refractory compositions available in the form of precast shapes have been employed. However, such products are not well suited for use as liners, crucible spouts and the like, because of their high density, or when available in the form of lightweight brick, because of their high cost. Moreover, the use of brick and other performed insulating materials is limited to relatively simple shapes and to applications which can accommodate the shape of the brick, such as in lining boilers, industrial furnaces and the like.
Although there are available refractory cements which can be cast in place, these materials normally have poor insulating characteristics at high temperatures, low strength, high density, or a combination of these properties which make their use undesirable. In an effort to increase the strength of these compositions and enhance their moldability, compositions containing fibrous material as the principal ingredient have been developed. These mixtures are made up, usually with water, to give fluidic compositions having densities ranging from 15 to 80 lbs./cubic foot. While these are easy to mold into the desired shape, they will shrink from 1 to 5% during drying, forming undesirable cracks in the final product and in some cases separating from the base material on which they are applied. There is a need, therefore, for a moldable insulating refractory composition that can be adjusted in density to permit maximum workability during application and that will adhere tenaciously to the surfaces commonly encountered in high temperature equipment. The composition should maintain its adhesion during drying and should set up to a relatively crackfree refractory mass which will retain its strength and adherence during subsequent heating operations up to the 1300.degree. C. range in high temperature applications.